Surface activation by plasma jets for thermal spray coating on cylinder bores

Abstract

A method of activating the surface of an aluminum-based substrate. This method includes cleaning the substrate surface, and operating a plasma spraying device such that a air plasma jet produced by the device is accelerated toward the surface so that it removes or decomposes any remaining oxides and other surface contaminants. In one form, the surface being treated forms part of a cylinder bore of an internal combustion engine block. In a particular form where a protective coating is subsequently being applied to the substrate, a sequential series of plasma spraying devices may be used such that a first—preferably simpler—device is used to perform activation or pretreatment operations, while a second—and more comprehensive—device may be used to deposit the protective layer on the pretreated surface.

Description

BACKGROUND OF THE INVENTION[0001]This invention is related generally to achieving better adhesion between a thermal sprayed protective coating and a target substrate, and in particular to pretreating the substrate with an air plasma spray prior to application of the protective coating.[0002]Thermal spray techniques have been shown to be an effective way to deposit protective coatings—such as thermal barrier coatings, wear coatings, anti-corrosion coatings or the like—onto a workpiece. The high deposition rates make such coating approaches amenable to large-scale manufacturing, such as that associated with the production of engine cylinder bores and the pistons that are designed to reciprocate in them. Adhesion of the protective coating to a substrate is a very important metric for determining the suitability of the coating for a particular application (such as for the harsh environments produced within the combustion chamber of an internal combustion engine cylinder bore). Tradition...

AI Technical Summary

Benefits of technology

This patent relates to a method of preparing a substrate, such as an engine cylinder bore, before applying a protective coating. The method involves using an air plasma jet produced from a plasma spraying apparatus to clean the surface and remove any oxides or contaminants that may affect the adhesion of the coating. The air plasma jet is accelerated towards the surface and decomposes or removes the oxides and contaminants, making the surface ready for the coating. This method simplifies the process and eliminates the need for separate mechanical activation steps, improving the long-term adhesion of the coating and avoiding the need for traditional mechanical activation approaches.

Problems solved by technology

While effective for their intended purpose, they add significant complexity and cost to the coated component's manufacturing process.

For example, mechanical roughening / locking-based approaches involve high tooling costs; these costs tend to be exacerbated by short tool life and extensive cleanup requirements.

Likewise, the high-pressure water jet blasting approach has very high capital costs, while the grit blasting approach has sand contamination problems, as well as (along with the mechanical roughening mentioned above) significant cleanup requirements.

Some of these cleanup requirements (as well as substrate pretreatment) may also use volatile organic compounds (VOCs) the use of which is coming under increasing scrutiny for their potentially negative environmental impact.

As with the substrate activation pretreatments mentioned above, this involves significant additional complexity and related cost.

While plasma spraying in general (and PTWA in particular) has been especially well-suited to coating the aforementioned engine cylinder bores, it has not been used for substrate activation as a way to improve the ordinarily weak bonding exhibited between the protective coating and the substrate.

Images